The present invention relates to a resin seal ring by injection molding, which is used for a hydraulic mechanism of an automatic transmission (AT), a continuously variable transmission (CVT) and a method of manufacturing the seal ring. More particularly, the present invention relates to a small seal ring, having an inner diameter not more than 20 mm, which can be incorporated in a mating shaft with a high mountability and a method of manufacturing the seal ring.
Nowadays an oil-sealing ring for sealing a hydraulic oil used much in the automatic transmission and the continuously variable transmission is formed by injection-molding a mixture of polyether ketone resin, a reinforcing component such as carbon fiber, a solid lubricant such as polytetrafluoroethylene (PTFE) resin, and the like. An abutment portion consisting of adjacent abutments is formed on the oil-sealing ring by cutting a portion thereof. A gate into which resin is injected is formed at a portion (mainly on inner peripheral surface) opposed to the abutment portion disposed at the center of the seal ring. The seal ring is fitted on a rotary shaft by expanding the abutments with a jig.
A known method of fitting the resin seal ring on a mating shaft (hereinafter referred to as merely shaft) is described below with reference to FIG. 4.
A resin seal ring 1 is fitted on a mating shaft 11 by using a tapered jig 4 as follows: After the seal ring 1 is fitted on the tapered jig 4 from a small-diameter side 4a thereof to a large-diameter side 4b thereof, the shaft 11 is inserted into the tapered jig 4. Thereafter the seal ring 1 is dropped into a seal ring-mounting groove 12 of the shaft 11 from the large-diameter side 4b of the tapered jig 4.
In fitting the seal ring 1 on the shaft 11, a strain is generated in the neighborhood of the position of the seal ring opposed to the abutment portion and a stress concentration occurs. Therefore when the seal ring 1 has a gate for injection molding use or a weld portion having a low mechanical strength at the position opposed to the abutment portion, the seal ring may be broken at the position opposed to the abutment portion. Another problem of the seal ring having the gate for the injection molding use at the position opposed to the abutment portion is that the orientation of reinforcing fibers such as carbon fibers disposed in the vicinity of the gate is parallel with the direction of a strain-caused crack. Thus it is impossible to obtain a sufficient reinforcing effect in the neighborhood of the gate. Therefore when the seal ring is fitted on the shaft, the seal ring is broken at the gate mark. In recent years, there is a tendency for the seal ring to be formed compactly because a hydraulic mechanism is becoming compact. The seal ring having an inner diameter of 20 mm or less is easily broken even though the seal ring is composed of a comparatively flexible material. Polyether ketone resin is known as a crystalline thermoplastic resin excellent in its heat resistance, mechanical property, self-lubricant property, and flexibility. The above-described problem of breakage is caused by deterioration of flexibility of the composition of the seal ring containing an inorganic reinforcing material such as carbon fibers which impart a demanded high wear resistance to the seal ring.
As a means for solving the above-described problems, resin is injected into a portion in the vicinity of one end of abutments of the seal ring disclosed in Japanese Patent Application Laid-Open No. 8-233110. In the method disclosed in Japanese Patent No. 3299419, the gate position is spaced at a certain interval from the position opposed to the abutment portion to prevent breakage of the seal ring.
However, the step cut portion is complicated in its configuration and demanded to have high precision to keep oil-sealing performance. Thus a telescopic construction is adopted for the step cut portion. Therefore a parting line which may cause generation of a burr is present on the periphery of the step cut portion. In the seal ring disclosed in Japanese Patent Application Laid-Open No. 8-233110, the gate to which a highest pressure is applied is disposed on the periphery of the step cut portion when molding operation is performed. Thus the burrs tend to be generated there.
In the seal ring disclosed in Japanese Patent No. 3299419, after the seal ring having the gate formed at a position spaced from the position opposed to the abutments, the abutment portion is formed by a mechanical processing as the means for avoiding breakage of the seal ring when it is fitted on the rotary shaft. However, the seal ring has the weld portion having a low strength. If the inner diameter of the seal ring is not more than 20 mm, the weld portion is liable to be broken by a shock applied to the seal ring when it is fitted on the rotary shaft. Supposing that the angle of the abutment portion of the seal ring is 180 degrees and the angle of the portion opposed to the abutment portion is 0 degree, the gate is disposed in the range of 45 to 90 degrees. However, the gate is not spaced sufficiently from the position where a large strain is generated when the seal ring is fitted on the rotary shaft. Thus the seal ring does not have any effect of improving fittability of the seal ring on the rotary shaft or has deteriorated fittability.